Australian police are searching for a nine-year-old boy who is believed to have been attacked by a crocodile and dragged out to sea.

The boy was swimming with a group of people at Port Bradshaw, in the Northern Territory, when he was attacked.

"Initial reports suggest adults within in the group tried to save the boy by spearing the animal, but the crocodile dragged the child out to deeper water," police Superintendent Michael White said in a statement.

Supt White said the incident highlighted the dangers of swimming in waterways in northern Australia.

Two weeks ago a seven-year-old girl was feared killed by a crocodile at a waterhole about 340km (210 miles) east of the city of Darwin, the capital of the Northern Territory.

Police searching the waterhole shot dead a three-metre (10ft) crocodile, and an examination of the animal revealed what were believed to be human remains in its stomach.

Saltwater crocodiles, which can be up to seven metres (23ft) long and weigh more than a ton, are a common feature of Australia's tropical north.

They have been protected since the 1970s and their numbers have increased steadily since.